1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, in which a monitor pattern is provided for accurate measurement of the thickness of an interlayer insulating film.
2. Background Art
In recent years, silicon integrated circuit devices have been miniaturized in a vertical direction less than in a horizontal direction. For this reason, recent semiconductor devices have become more three-dimensional, and an absolute step becomes larger in the scale of a chip or wafer.
With a view to miniaturizing semiconductor memory while ensuring an increase in the capacitance of a capacitor, memory cells become more three-dimensional, and a large step arises between the memory cells and peripheral circuits. In an integrated logic circuit, wiring patterns are multilayered in order to improve the performance and speed of the logic circuit. As a result, a step is formed between an area where wiring patterns are densely formed and an area where wiring patterns are sparsely formed. Such a step poses a serious problem in transferring a pattern on a substrate.
With regard to the pattern transfer technique, an increase in resolving power imposes a problem of a shallow depth of focus. The depth of focus becomes significantly small as a result of an increase in the aperture of a lens or of a reduction in the wavelength of light. Such a reduction in the depth of focus presents a problem in miniaturizing a semiconductor device as the device becomes more three-dimensional. If an attempt is made to miniaturize the semiconductor device to a much greater extent, a polarization technique for smoothing the absolute step must be adopted into the pattern transfer process in order to enable a pattern to be transferred at a small depth of focus.
Conventionally-employed techniques for smoothing an inter-layer insulation film, such as SOG or BPSG reflow techniques, are for local smoothing, e.g., an area of micrometers. For this reason, it is impossible to smooth the absolute steps in the scale of a chip or wafer using these techniques. For the time being, it is only possible to use a chemical mechanical polishing method.
To respond to such a demand, a chemical mechanical polishing method (hereinafter often referred to as a CMP or a CMP method) such as that shown in FIG. 7 has already been proposed [see Japanese Patent Publication (Tokyo Koho) No. 5-30052 or Japanese Patent Application Laid-open (Kokai) No. 7-285050].
In FIG. 7, reference numeral 111 designates a rotary table (or platen); 112 designates an abrasive cloth; 113 designates a semiconductor wafer having an insulating film formed thereon; 114 designates packing material; 115 designates an abrasive head; and 116 designates an abrasive agent. The abrasive cloth 112 is attached to the rotary table 111 with an adhesive, and the rotary table 111 rotates around a spindle. The packing material 114 is fixed on the abrasive head 115 with an adhesive. The semiconductor wafer 113 having an insulating film is attached to the packing material 114 with the surface of the insulating film facing down by means of vacuum chucking or surface tension of water.
An actual abrasive method will be described by reference to FIG. 7. In FIG. 7, the rotary table 111 is rotated around the spindle, and the abrasive head 115 is also rotated around another spindle. While the abrasive agent 116 is applied to the surface of the abrasive cloth 112 at a given flow rate, the abrasive head 115 is pressed against the abrasive cloth 112 at a given pressure, whereby the surface of the insulating film of the semiconductor wafer 113 is abraded.
FIGS. 8A to 8F are illustrations for explaining an example of an actual abrasive process which uses such a CMP method. In FIGS. 8A to 8F, reference numeral 21 designates a silicon substrate; 22 designates an oxide film; 23 designates a first diffused layer; 24 designates a nitride film; 25 designates a silicon electrode; 26 designates a second diffused layer; 27 designates an insulating film provided below a wiring pattern (hereinafter simply referred to as an insulating film); 28 designates a first metal wiring layer; 29 designates an interlayer insulating film; and 30 designates a second metal wiring layer.
The nitride film mask 24 is formed on the silicon substrate 21, and the oxide film 22 and the first diffused layer 23 are formed on the nitride film mask (FIG. 8A). The silicon electrode 25 and the second diffused layer 26 are formed on the oxide film 22 (FIG. 8B). After formation of the insulating film 27, a contact hole is formed in the insulating film, and the first metal wiring layer 28 is formed on the insulating film 27 (FIG. 8C). The interlayer insulating film 29 is formed on the first metal wiring layer 28 and the insulating film 27 (FIG. 8D). Subsequently, the interlayer insulating film 29 is smoothed through use of the foregoing chemical mechanical polishing method (FIG. 8E). After a through hole has been formed in the interlayer insulating film, the second metal wiring layer 30 is formed on the interlayer insulating film (FIG. 8F).
At this time, in terms of product control, the thickness of a film, the amount of abrasion, and the thickness of a film after abrasion must be controlled by measuring the thickness of the interlayer insulating film 29 from above an aluminum wiring pattern.
To this end, a pattern for the purpose of measuring film thickness is formed in a scribe line, and the thickness of a film before and after abrasion is usually controlled through use of the thus-formed pattern.
FIG. 9 is a schematic representation showing an example of layout of a monitor pattern for the purpose of measuring film thickness conventionally formed in a semiconductor wafer. In the drawing, reference numeral 1 designates a semiconductor wafer; 3 designates a scribe line area (hereinafter also referred to as a scribe line, as required); 5 designates a chip formed on the semiconductor wafer 1; and 9 designates a monitor pattern for the purpose of measuring film thickness formed in the scribe line 3.
Under the foregoing chemical mechanical abrasive method, the flatness of a film is dependent on a pattern formed thereon. In short, it takes a longer time to smooth steps as the pattern becomes broader and denser. In the case of a semiconductor device--in which patterns are densely formed over a broad area within a chip--such as DRAM or a DRAM-mixed logic IC, a result which is obtained by measurement of thickness of the film using the film-thickness monitor pattern 9 of the scribe line does not necessarily match the thickness of a circuit portion of the film actually measured. Such a discrepancy in thickness poses a problem of deterioration of reliability of CMP process control.